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Canine Anaplasmosis

Canine Anaplasmosis

 

Andy Pachikerl, Ph.D

 

Introduction

Anaplasma platys (formerly Ehrlichia platys) is a Gram negative, non-mobile, pleomorphic bacterium, belonging to the Anaplasmataceae  family, which has been speculated, but not conclusively demonstrated, to be transmitted by Rhipicephalus sanguineus, known as the “brown dog tick” (Simpson et al. 1991). Anaplasma platys is an obligate intracellular microorganism, which appears to parasitise dog platelets exclusively, causing a Canine Vector-Borne Disease (CVBD) named Infectious Canine Cyclic Thrombocytopenia (ICCT) (Cardoso et al. 2010) due to the thrombocytopenia that relapses every 7-14 days (Harrus et al. 1997).

 

Since its first identification in Florida (Harvey et al. 1978), A. platys infection has been reported in several countries around the world, including the United States, China, Thailand, India, Japan, Venezuela, Brazil, Chile, Israel and Australia (Abarca et al., 2007, Abd Rani et al. 2011, Brown et al. 2001, Cardozo et al. 2009, French et al. 1983, Hua et al. 2000, Inokuma et al. 2001, Suksawat et al. 2001). With regard to Europe, the presence of A. platys has been reported in France, Italy, Spain, Greece, Portugal, and Croatia and in 2 dogs imported in Germany (Beaufils et al. 2002, De La Fuente et al. 2006, Dyachenko et al. 2012, Ferreira et al. 2007, Kontos et al. 1991).

 

Despite the increasing interest in Vector Borne Pathogens (VBPs) affecting dogs in Italy (Dantas‑Torres et al. 2012), the infection by A. platys is poorly documented and considered to be sporadic throughout the country. Nonetheless, A. platys has been serologically and molecularly detected in dogs from Southern regions (Sicily, Apulia and Abruzzo), mostly in co-infection with other VBPs (16, 17, 35, 37,39). Moreover, the DNA of this pathogen has also been found in R. sanguineus ticks by PCR (Sparagano et al. 2003).

 

Diagnosis

Blood tests and a urinalysis are the main diagnostic tools for anaplasmosis. The blood tests usually include a complete blood count, blood smear evaluation, biochemistry panel, serology to look for antibodies, and polymerase chain reaction (PCR) assays. If the dog is lame, radiographs and analysis of joint fluid are usually included.

 

Among the current available diagnostic methods for detection of A. platys infection, the most used include morulae identification in the blood smears, antibody detection and DNA amplification by PCR (Otranto et al. 2010). Demonstration of the intra-platelet inclusion bodies of A. platys on blood or buffy-coat smears commonly represents the first diagnostic approach in A. platys infection, especially during the acute phase of disease. On the basis of the study described in this article, an accurate, light microscopy analysis of the stained blood smears appears to be a reliable method to point the diagnosis in the direction of A. platys infection, as it allowed platelet cytoplasmic inclusions resembling A. platys morulae to be detected and acute infection to be suspected in all 3 clinical cases. However, a definitive detection of the organisms in blood films may be difficult and cannot be considered a reliable diagnostic method in the chronic phase of the infection due to the cyclic course of bacteraemia, the rarely found parasitaemia and the fairly frequent presence of a very low number of infected platelets (Harrus et al. 1997, Otranto et al. 2010). Furthermore, it should be considered that inclusion bodies within platelets may be present and related to platelet activation during inflammation and E. canis infection and, thus, misdiagnosed as A. platys morulae (Ferreira et al. 2007).

 

Serological methods, such as IFAT, were not taken into account in the diagnostic approach of A. platys infection because they are uncommonly applied, due to the difficulty in obtaining A. platys-infected platelets to use as antigen (A. platys has not yet been cultured) (Lai et al. 2011, Martin et al. 2005) and the possible false-positive results linked to the serologic cross-reactivity between organisms belonging to the same sero-group (e.g. A. phagocytophilum). Recently, a simple qualitative in-clinic Enzyme Linked Immunosorbent Assay (ELISA), the Snap®4Dx Plus (IDEXX Laboratories, Westbrook, ME, USA) was developed in order to identify antibodies against A. platys, as well as to detect Dirofilaria immitis antigen and antibodies for further VBPs e.g. A. phagocytophilum, E. canis, E. erwiingi, B. burgdorferi. Similarly, some rapid tests developed by bioguard or biogen also detect the antibodies against A. platys and other VBP. Thess rapid tests gained favour among small-animal practitioners due both to its ease of use and its accuracy; however, is not able to distinguish between A. phagocytophilum and A. platys. Moreover, the presence of anti-A. platys antibodies does not mean clinical infection, but rather exposure to the infectious agent (Martin et al. 2005).

 

Recently, more specific and sensitive strategies focusing on molecular methods based on PCR approaches were employed (Eddlestone et al. 2007, Ferreira et al. 2007, Inokuma et al. 2002, Lai et al. 2011, Martin et al. 2005) to enable the diagnosis of active cases of A. platys infection, which would otherwise have gone undetected due to low‑sensitivity of microscopy and the low-specificity of the serological diagnosis. It has been demonstrated that PCR is positive even in the case of low-level parasitaemia (Otranto et al. 2010). Several PCR assays were optimized to allow for accurate identification of A. platys infection in dogs using different targets (16S rRNA, p44, groESL, gltA). Therefore, the PCR test, confirmed by a sequence analysis of amplicons, is the most reliable diagnostic test for this pathogen to date (Aguirre et al. 2006, De La Fuente et al. 2006, Gaunt et al. 2010).

 

Treatment

Treatment includes antibiotics, pain relievers, and anti-inflammatory drugs.

 

Doxycycline is the most used antibiotic. Most dogs respond within one to two days after they first take doxycycline. Other antibiotic options are tetracycline or minocycline.

 

Analgesia and anti-inflammatory drugs may be needed for joint pain. Let your veterinarian choose the anti-inflammatory, rather than choosing and dosing it yourself, because dogs metabolize these medicines differently than humans do. Your veterinarian will have the most appropriate medication.

 

Disease Prevention

Appropriate tick control is critical to preventing this disease. Preventing ticks from attaching and removing any ticks from your pet within a few hours of attachment is vital.

 

Note: Dogs with anaplasmosis may also be infected with other tick-borne organisms (Ehrlichia, Borrelia, etc.), so infected dogs should be screened for those diseases also.

 

Granulocytic Anaplasmosis

Granulocytic anaplasmosis is an infection of white blood cells. It is caused by Anaplasma phagocytophilum.

Ixodes pacificus (commonly called the Western blacklegged tick) is the primary vector in the Western United States. Photo by Dr. Cathy Wilkie.

 

Anaplasma phagocytophilum is transmitted via a bite from an Ixodes tick. Ixodes scapularis (often commonly called the deer tick, blacklegged tick, or bear tick) is the primary vector in the Midwest and North-eastern United States; Ixodes pacificus (commonly called the Western blacklegged tick) is the primary vector in the Western United States; and Ixodes ricinus (commonly called the castor bean tick) is the primary vector in Europe.

 

Granulocytic anaplasmosis is seen most in dogs in the North-eastern, upper Midwest, and coastal western United States. Since granulocytic anaplasmosis requires the Ixodes tick as its vector, seasonal outbreak of the disease can occur from spring through summer. Clinical disease is most often seen in adult dogs, and golden retrievers and Labrador retrievers appear to get it more than other breeds.

 

A. phagocytophilum can infect a wide range of mammals. In addition to dogs, clinical disease has been documented in cats, cattle, sheep, goats, llamas, and humans.

 

Because of common vectors and rodent reservoirs, co-infection with Borrelia burgdorferi can be seen and can lead to more severe illness.

 

Many dogs exposed to granulocytic anaplasmosis do not get obvious signs of the condition. If signs are seen, they most often occur during the acute phase of infection, which is 1 to 2 weeks after transmission. The signs may be vague and include lethargy, lack of appetite, and fever. Some dogs may become lame because their joints are painful. Less common signs include vomiting, diarrhoea, coughing, and difficulty breathing.

 

The prognosis for granulocytic anaplasmosis is quite good.

 

Infectious Cyclic Thrombocytopenia

Infectious cyclic thrombocytopenia is an infection of blood platelets. It is caused by Anaplasma platys.

 

Anaplasma platys transmission has not been fully determined, although tick vectors are probable. The organism has been found in Rhipicephalus and Dermacentor ticks.

 

Signs include lack of appetite, lethargy, fever, bruising on the gums and stomach, nosebleeds, and weight loss.

 

Many dogs with infectious cyclic thrombocytopenia have only mild clinical disease, so prognosis is generally good.

 

Other complications

Common haematological abnormalities recorded in 3 dogs included mild to moderate thrombocytopenia with increased MPV, moderate to severe normocytic normochromic anaemia and evidence of giant platelets on blood films, these findings are consistent with experimental (Baker et al. 1988, Gaunt et al. 2010) and natural infections (Beaufils et al. 2002, De Caprariis et al. 2011) of A. platys. At the beginning of the disease, the fundamental mechanism of thrombocytopenia and thrombocytopathy, found in both single and co-infections with A. platys, may be attributed mainly to the direct action of the parasite (increased platelet consumption, production of inhibitory factors) and, at a later stage, to the hypersplenism or immunologically mediated platelet destruction stimulated by the bacteria (Baker et al. 1988, De Caprariis et al. 2011, Harvey et al. 1978).

 

The immune mediated phenomena and particularly IMHA, have been previously observed in dogs infected by A. phagocytophilum and E. canis (Bexfield et al. 2005, Harrus et al. 1999, Mazepa et al. 2010), whereas they have never before been described in dogs infected by A. platys. Some authors stated that dogs affected with bacterial infection and IMHA are prone to the development of thromboembolic complications with consequent negative course of the disease (Carr et al. 2002). The occurrence of the disseminated intravascular coagulation (DIC) observed in dogs 2 and 3 probably exasperated the overall clinical conditions of the animals, bringing to their death in absence of a prompt anticoagulant prophylaxis. In this respect, it is significant that the symptomatology in dog 1, which showed no immune-mediated complication, rapidly regressed after therapy as also observed by other authors (Beaufils et al. 2002, Eddlestone et al. 2007, Gaunt et al. 2010).

 

References:

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